Personally I think this rumor is laughable, in an industry where everyone is switching to turbo or hybrid power plants there's NO WAY the next m5 will have a NA V10. NA motors are a thing of the past (sadly) even Ferrari announced there not making them anymore.
The only way it will be a V10 is if it's turbo...and then we'll get to listen to everyone complaining about the sound compared to the NA V10
